Alcohol has long been known to cause suppressive effect on immune responses. Chronic consumption of alcohol is often associated with a higher frequency of chronic infection with agents such as hepatitis C virus. However, the precise molecular mechanism for how alcohol suppresses immune response is currently not clearly identified. One of the endogenous molecules affected by alcohol is phospholipase D (PLD). PLD is an enzyme that catalyzes hydrolysis of phosphatidyl choline, a major phospholipid found in lipid bilayers, into phosphatidic acid (PA) and choline. PA is an active second messenger that recruits and activates its target proteins. In the presence of alcohol, particularly primary alcohol (1-alcohol) such as ethanol and 1-butanol, PLD catalyzes transphosphatidylation instead of hydrolysis. As a result, production of PA is significantly reduced when 1-alcohol is present. Our preliminary studies demonstrate that, in the presence of 1-alcohol, antigen receptor- induced proliferation of CD4? effector T cells was severely impaired while expansion of CD4? remains intact. As a consequence, T cells expanded in the presence of 1-alcohol were markedly enriched for regulatory T cells that impose suppressive effects on immune responses both in vitro and in vivo. Similar effect was observed by gene knockdown of PLD. Based on these data, we hypothesize that PLD is a target of alcohol-induced enrichment of Tregs. In this study, we will use our recently established conditional gene knockout mice of PLD1 and PLD2 gene and determine if PLD signal inhibition makes T cells more sensitive to alcohol induced Treg enrichment both in vitro and in vivo. Successful completion of this study will contribute to better treatment of infectious diseases among heavy alcohol consumers. Moreover, it may provide potential procedures for enrichment of regulatory T cells and help the treatment of autoimmune disease and tissue transplantation. PUBLIC HEALTH RELEVANCE: This project will help understanding the mechanism by which alcohol suppresses immune responses and may help developing a new tool to develop treatment for autoimmune disorders using alcohol. Our preliminary data show that exposure of lymphocytes causes enrichment for immunosuppressive subset of cells. This study will analyze is this effect is mediated by inhibition of an enzyme called phospholipase D using genetically manipulated mice that lack expression of this enzyme.